The present invention relates to medical stimulators and leads generally, and more particularly to implantable atrial anti-arrhythmia pacemakers.
In conjunction with stimulators which treat atrial arrhythlnias, it is often beneficial to include the capability of delivering high rate atrial pacing pulses, either for therapeutic purposes to terminate detected atrial arrhythmias or for electrophysiologic screening purposes to induce and terminate arrhythmias under physician control. In most patients, during an atrial tachyarrhythmia or during rapid atrial pacing, atrial depolarizations are effective to trigger ventricular depolarizations sufficient to provide a ventricular rate adequate to support the patient. However, in the context of patients having total or intermittent AV block, their ventricular rate may drop to an extremely low level during atrial anti-tachycardia pacing or during rapid atrial stimulation for testing purposes, in the absence of backup ventricular pacing. For this reason, atrial anti-tachycardia pacemakers and defibrillators have employed ventricular back-up pacing in conjunction with rapid atrial pacing.
For example, during temporary high rate atrial pacing, the Intermedics Relay TM pacemaker can provide ventricular pacing at a selected multiple of the atrial escape interval. In other words, in the presence of rapid atrial pacing, a ventricular pacing pulse may be delivered once every X atrial pacing pulses. A similar feature is available in the Medtronic Thera.RTM. pacemaker, presently marketed by Medtronic.
In defibrillators, it has also been proposed to provide ventricular back-up pacing in conjunction with rapid atrial pacing used for electrophysiologic screening purposes. For example, demand VVI pacing as a backup to rapid atrial pacing is provided in the Ventak AV Model 1810 and 1815 implantable cardioverter/defibrillators presently sold by Cardiac Pacemakers, Inc. Back-up VVI pacing is also proposed in U.S. Pat. No. 5,653,737 issued to van Lake.
The back-up ventricular pacing provided in the Intermedics Relay and Medtronic Thera.RTM. devices is asynchronous to the underlying ventricular rhythm, the ventricular sense amplifier being disabled during delivery of rapid atrial pacing pulses. In the Ventak AV, however, ventricular demand pacing is provided at a programmed pacing rate, as also suggested in the above cited U.S. Pat. No. 5,653,737. In both of these patents, however, the escape interval is apparently set independent of the delivery of atrial pacing pulses as well as independent of the underlying ventricular rate of the patient. In the context of providing back-up ventricular pacing during rapid atrial pacing, however, it should be noted that sensing ventricular depolarizations may often be difficult due to the requirement that the ventricular sense amplifier be blanked in conjunction with delivery of atrial pacing pulses. Due to the difficulty of sensing in the ventricle during delivery of high rate atrial pacing pulses, the potential for competition between delivered ventricular pacing pulses and the patient's underlying ventricular rate remains substantial using either approach.